No need to make this complicated – it’s a router jig that’ll cut circles. It’ll be useful for anything involving fretboard radius (also required for this compound-radius jig), and it’s generally a good thing to know about for a lot of carpentry projects as well.
Speaking of making things too complicated, this design can be simplified to two boards and a screw if you’re not interested in having this thing take up space. As long as your measurements are correct, everything will work out just fine!
That’s all there is to it! Make sure you’re measuring you’re radius distances from the center of the dowel hole where your swinging board attaches to the bottom of the router bit. If the bit is 1/2″ diameter, you can measure and mark your radius 1/4″ longer so you can center the bit. That’s all there is to it!